Cable transmissions are commonly used in robotics for remote force transmission, offering a lightweight, compact, and efficient solution for transmitting high forces between input and output. However, cables in flexible compression housings (Bowden cables), exhibit high static friction, which increases exponentially with total bend angle. Alternatively, internally routed ball-bearing supported cable capstan transmissions are low friction, but complex and present challenges in routing multiple sets of cables. In this paper, we propose motion-decoupled cable transmission modules that address these challenges, occupying the middle ground, functioning as discrete-joint ball-bearing supported Bowden cables. Our rolling-plus-twist joint design decouples pairs of routed cables from changing significantly in tension, length, or friction during large angle motion of the linked transmission. Using sub-1 mm diameter high-strength synthetic cable, the transmission exhibits a maximum coupling motion of only 0.15 mm over the full range of motion of the cable-transmission mechanism, approximately 10% of pretension in combined hysteresis and friction, a transmission stiffness of 10 N/mm, weighing just 9 g per rolling joint and 5 g per twist joint. Two applications are demonstrated: cable routing alongside a robot arm for, say, gripper remote actuation, and remote needle advancement for an MRI-safe needle biopsy robot.

We present admittance control and fingertip contact detection with a linkage gripper remotely driven by a pneumatic rolling diaphragm actuator. The gripper is driven by underactuated mechanisms sensorized by joint encoders in order to fully determine the gripper state. We present the modelling of the linkage and fluidic transmission, validate its ability to regulate pinch force via admittance control within an RMS error well under 0.5 Newtons, and show the ability to detect contact at targeted locations on the linkage. In addition, we demonstrate simple grasping behaviors: blindly searching for an unobstructed object and detecting object loss. Our results show that an integrative approach of instrumenting underactuated gripper mechanisms can result in a lightweight gripper that is not only mechanically adaptive but sensitive enough to react to contact events without distal sensors or vision.

Contact detection without endpoint tactile sensing is challenging; friction and inertia obscure the sensing of low amplitude and high frequency forces. In this work we explore fluidic transmissions as series-elastic actuators, coupled to remotely-located direct-drive brushless motors, in a bid to maximize low-impedance sensitivity to contact while maintaining high bandwidth. We employ a disturbance observer to remove motor friction and further reduce minimum impedance. Using a 2-DOF remotely-actuated hydraulically-coupled robotic gripper, we demonstrate a maximum endpoint Z-width of 40dB and a robust contact detection threshold of 0.2N, without endpoint tactile sensing or joint position sensing. These results enable wiring-free and joint sensor-free arm and end-effector design, which are of particular interest for human-robot interaction, harsh-environment, magnetically-sensitive, and low-cost robotic manipulators that must maintain high bandwidth and high contact sensitivity.

This paper reports on Team Northeastern's Avatar system for telepresence, and our holistic approach to meet the ANA Avatar XPRIZE Final testing task requirements. The system features a dual-arm configuration with hydraulically actuated glove-gripper pair for haptic force feedback. Our proposed Avatar system was evaluated in the ANA Avatar XPRIZE Finals and completed all 10 tasks, scored 14.5 points out of 15.0, and received the 3rd Place Award. We provide the details of improvements over our first generation Avatar, covering manipulation, perception, locomotion, power, network, and controller design. We also extensively discuss the major lessons learned during our participation in the competition.

Real-time magnetic resonance imaging (MRI) in-terventions are significantly impacted by material compatibility problems and size constraints in the MRI bore. Limited physi-cian access to patients within the bore of the MRI necessitates iterative positioning and imaging, which prolongs the duration of the procedure and increases patient risk. We present a passive MR-safe haptic teleoperation device for prostate needle biopsy inside an MRI machine. The device uses a low-friction hydrostatic transmission based on paired rolling diaphragm actuators, linear and rotary. The device has two degrees of freedom, allowing needle insertion and rotation. The robot produces negligible MR imaging artifacts, has effective positioning tracking, and can reliably detect needle punctures in the clinically relevant range. We describe the design components, system transparency, and perform a needle insertion test.

There has been a drastic shift to remote interaction for professional, industrial and personal interactions. Improving the overall quality of these interactions by removing any sense of distance between the users is the ultimate goal. Video conferencing has been widely adopted as an improvement to audio-only interactions. Having added visuals to audio communication, the next frontier is to add physical interaction to this remote communication. In this paper, we present an avatar system with the aim of tackling these necessities. The proposed system includes both hardware and software designs to ensure a real-time telemanipulation experience with tactile force feedback. We present a coupled hydrostatic actuated gripper and glove with high system bandwidth to reduce the inherent latency of the mechanical system. To account for latency over the network, the wave variable based method is adopted to maintain the stability of the closed-loop gripper control even under hundreds of milliseconds of delay. A bidirectional audiovisual communication system comprised of off-the-shelf hardware and software is incorporated to allow realtime conversation between the operator and the recipient for collaborative tasks. the proposed system has been validated in lab experiments and the global ana avatar xprize challenge semifinal.

Localizing and tracking the pose of robotic grippers are necessary skills for manipulation tasks. However, the manipulators with imprecise kinematic models (e.g. low-cost arms) or manipulators with unknown world coordinates (e.g. poor camera-arm calibration) cannot locate the gripper with respect to the world. In these circumstances, we can leverage tactile feedback between the gripper and the environment. In this paper, we present learnable Bayes filter models that can localize robotic grippers using tactile feedback. We propose a novel observation model that conditions the tactile feedback on visual maps of the environment along with a motion model to recursively estimate the gripper's location. Our models are trained in simulation with self-supervision and transferred to the real world. Our method is evaluated on a tabletop localization task in which the gripper interacts with objects. We report results in simulation and on a real robot, generalizing over different sizes, shapes, and configurations of the objects.

Dexterous, serial-chain motor-driven robotic arms have high moving mass, since most of the actuators must be located in the arm itself. This necessitates high gear ratios, sacrificing passive compliance, backdrivability, and the capacity for delicate motion. We introduce the concept of a remote direct-drive (RDD) manipulator, in which every motor is located in the base, connected to remote joints via a low-friction hydrostatic transmission. We have designed a new hydrostatic linear actuator with a fully-floating piston; the piston floats within the cylinder using a pair of soft fiber-elastomer rolling-diaphragm seals. This eliminates static friction from seal rubbing and piston/rod misalignment. Actuators were developed with a 20mm bore, weighing 55 grams each with a 400:1 bidirectional strength-to-weight ratio $( + /-230\mathrm {N}$), which drive a 2-DOF manipulator (wrist pitch/finger pinch; 120-degree range-of-motion; 6.6 Nm max grip strength). The gripper is hydrostatically coupled to remotely-located direct-drive/backdrivable brushless electric motors. System hysteresis and friction are 1 percent of full-range force. This low-mass low-friction configuration is of great interest for powered prosthetic hand design, and passively-safe high dynamic range robot arms.

Magnetic resonance imaging (MRI) offers many benefits, including unsurpassed soft-tissue characterization and the ability to combine detection and biopsy into a single procedure. However, limited patient access in the narrow scanner bore requires tedious iterative positioning or use of robotic assistants that isolate the physician from the patient. As an alternative, we present a teleoperation technology for percutaneous procedures to meet the needs of interventional radiologists and overcome challenges imposed by the MR environment. The technology is demonstrated for a 1-DOF needle insertion procedure. The technology uses rolling diaphragms, a clutch, and a cable-capstan drive to propel the needle while relaying forces and motions to the operator. The system demonstrates excellent position tracking (< 0.7° error in the unloaded case) and reliably transmits changes in force. During needle teleoperation, users were able to detect light membrane punctures and differentiate spring stiffnesses nearly as accurately as by hand manipulation.

We present a new type of hydrostatic transmission that uses a hybrid air-water configuration, analogous to N+1 cable-tendon transmissions, using N hydraulic lines and 1 pneumatic line for a system with N degrees of freedom (DOFs). The common air-filled line preloads all DOFs in the system, allowing bidirectional operation of every joint. This configuration achieves the high stiffness of a water-filled transmission with half the number of bulky hydraulic lines. We implemented this transmission using pairs of rolling-diaphragm cylinders to form rotary hydraulic actuators, with a new design achieving a 600-percent increase in specific work density per cycle. These actuators were used to build a humanoid robot with two 4-DOF arms, connected via the hydrostatic transmission to an identical master. Stereo cameras mounted on a 2-DOF servo-controlled neck stream live video to the operator's head-mounted display, which in turn sends the real-time attitude of the operator's head to the neck servos in the robot. The operator is visually immersed in the robot's physical workspace, and through the bilateral coupling of the low-impedance hydrostatic transmission, directly feels interaction forces between the robot and external environment. We qualitatively assessed the performance of this system for remote object manipulation and use as a platform to safely study physical human-robot interaction.

The Harvard Robobee is a fly-sized aerial vehicle that can perform controlled flight maneuvers. But this robot is unable to control its yaw or heading angle to a desired value. Motivated by this deficiency, we propose a new method to produce yaw-axis rotations. Termed wriggle-steering, it consists of driving body oscillations around its two other rotational axes. Because no torque is applied directly around the controlled axis, it therefore constitutes an alternative control method for under-actuated designs. Oscillations are driven around pitch and roll axes at the same frequency but 90 degrees out of phase, resulting in a small change in yaw angle after each cycle because of nonlinearity in attitude dynamics. We propose two wing kinematics perturbations that produce the necessary actuation. The predictions are validated with a quasi-steady aerodynamics model, free-body simulations, and flight tests on a fly-sized hovering aerial robot. The results suggest that wriggle-steering can save mass and reduce complexity by eliminating the need for additional actuators in flapping-wing robots or other aircraft.

When designing a robot for human-safety during direct physical interaction, one approach is to size the robot's actuators to be physically incapable of exerting damaging impulses, even during a controller failure. Merely lifting the arms against their own weight may consume the entire available torque budget, preventing the rapid and expressive movement required for anthropomorphic robots. To mitigate this problem, gravity-counterbalancing of the arms is a common tactic; however, most designs adopt a shoulder singularity configuration which, while favorable for simple counterbalance design, has a range of motion better suited for industrial robot arms. In this paper we present a shoulder design using a novel differential mechanism to counterbalance the arm while preserving an anthropomorphically favorable singularity configuration and natural range-of-motion. Furthermore, because the motors driving the shoulder are completely grounded, counterbalance masses or springs are easily placed away from the shoulder and low in the torso, improving mass distribution and balance. A robot arm using this design is constructed and evaluated for counterbalance efficacy and backdrivability under closed-loop force control.

We present a passive fluid transmission based on antagonist pairs of rolling diaphragm cylinders. The transmission fluid working volume is completely sealed, forming a closed, passive system, ensuring input-output symmetry and complete backdrivability. Rolling diaphragm-sealed cylinders provide leak-free operation without the stiction of a traditional sliding seal. Fluid pressure preloading allows for bidirectional operation and also serves to preload the gears or belts in the linear-to-rotary output coupler, eliminating system backlash end-to-end. A prototype transmission is built and tested for stiffness, bandwidth, and frictional properties using either air or water as working fluids. Torque transmission is smooth over the entire stroke and stiction is measured to be one percent of full-range torque or less. We also present a tendon-coupled design where the rolling diaphragm is inverted from its normal orientation; this design does not require shaft support bushings, tolerates misalignment, and can be made out of substantially soft materials. Actuator units and a passive transmission are demonstrated using this new soft cylinder design.

Wing motion in most flapping-wing micro air vehicles (MAVs) is restricted to a flat stroke plane in order to simplify analysis and mechanism design. An MAV actuation and transmission design capable of controlling flapping motions and deviations from the mean stroke plane using relatively simple modifications to a proven design is presented. This allows preliminary investigation into more power-efficient wing trajectories, an important concern for small MAVs. A theoretical quasi-steady model of flapping wing flight is used to predict wing motions, and these predicted trajectories are compared to empirically observed trajectories from a test device. The ratio of average lift to average aerodynamic power is used as an efficiency metric to compare stroke trajectories.

Flapping-wing mechanisms inspired by biological insects have the potential to enable a new class of small, highly maneuverable aerial robots with hovering capabilities. In order for such devices to operate without an external power source, it is necessary to address a complex system design challenge: the integration of all of the required components on board the robot. This paper discusses the flight energetics of flapping-wing robotic insects with the goal of selecting design parameters that enable power autonomy and maximize flight time. The subsystems of the robot are analyzed both from a broad perspective and using a detailed set of models for a piezoelectrically driven two-wing design. The models are used to perform a system-level optimization for the maximum flight time permitted by current technology, compare the resulting robot configurations to biological insects across several key metrics, and discuss the effect of performance gains in various subsystems of the robot.